A051913 -id:A051913 - cp's OEIS frontend

A066962 Duplicate of A051913.

Original entry on oeis.org

7, 9, 13, 14, 18, 19, 21, 26, 27, 28, 35, 36, 37, 38, 39, 42, 45, 52, 54, 56, 57, 63, 65, 70

Offset: 1

dead

A067020 Duplicate of A051913.

Original entry on oeis.org

7, 9, 13, 14, 18, 19, 21, 26, 27, 28, 35, 36, 37, 38, 39, 42, 45, 52, 54, 56, 57, 63, 65, 70

Offset: 1

dead

A125866 Odd numbers k such that cos(2*Pi/k) is an algebraic number of a 3-smooth degree, but not 2-smooth.

Original entry on oeis.org

7, 9, 13, 19, 21, 27, 35, 37, 39, 45, 57, 63, 65, 73, 81, 91, 95, 97, 105, 109, 111, 117, 119, 133, 135, 153, 163, 171, 185, 189, 193, 195, 219, 221, 243, 247, 259, 273, 285, 291, 315, 323, 327, 333, 351, 357, 365, 399, 405, 433, 455, 459, 481, 485, 487, 489

Offset: 1

Artur Jasinski, Dec 13 2006

nonn

Odd terms of A051913.
This sequence is infinite (unlike A004729), because it contains any A058383(n) times any power of 3.
A regular polygon of a(n) sides can be constructed if one also has an angle trisector.

Robert Israel, Table of n, a(n) for n = 1..10000

Cf. A004729, A051913, A058383, A125867-A125878.

filter:= proc(n) local r,a,b;
  r:= numtheory:-phi(n);
  a:= padic:-ordp(r,2);
  b:= padic:-ordp(r,3);
  if b = 0 then return false fi;
  r = 2^a*3^b;
end proc:
select(filter, [seq(i,i=3..1000,2)]); # Robert Israel, May 11 2020

Do[If[Take[FactorInteger[EulerPhi[2n+1]][[ -1]], 1]=={3},Print[2n+1]],{n,1,10000}]

Edited by Don Reble, Apr 24 2007

cp's OEIS Frontend

A066962 Duplicate of A051913.

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A067020 Duplicate of A051913.

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A125866 Odd numbers k such that cos(2*Pi/k) is an algebraic number of a 3-smooth degree, but not 2-smooth.

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